1. Field of Disclosure
The disclosure generally relates to communication systems and, more particularly, to a method for reducing interference in mobile networks.
2. Related Art
For many communication applications, high gain antennas are used to improve performance. For example, high gain antennas are used to improve the performance of microwave links used for commercial telephony and satellite links. In most applications, the antenna beam points to a single communication node, such as a satellite or an aircraft. Different antenna beams may use the same frequency as long as the antenna beams do not overlap spatially.
However, situations may exist while a high-grain antenna at node A may be used to communicate with a communication node B, while one or more other communication nodes, C and perhaps D, are within the beam width of the high-gain antenna signals sent from communication node A to communication node B, in this case, the signals being sent from communication node A to communication node B may block communications being sent to, or between, the other communication nodes C and D.
Several approaches have been tried in an attempt to mitigate this problem. In a first approach, static off-axis pointing is used. For example, the high-gain antenna at communication node A is aimed so that communication node B with which it is communicating is slightly off the axis of the antenna beam, and a null in the antenna pattern is aimed at the communication node C. Although this approach minimizes interference to and from communication node C, the approach is performed using trial and error. Typically, the antenna is adjusted (often manually) until the signal to or from communication node B is optimized and interference to or from communication node C is minimized. This approach is too slow to respond to the dynamics of highly mobile transmitters and receivers.
In a second approach, the location and transmit power of a plurality of communication nodes is monitored by a control node. For example, the control node is in communication with all communication nodes A and includes the capability to calculate the total power reaching each adjacent communication node C from all communication nodes A. The control node commands some communication nodes A which it controls to reduce the power and data rate of their transmissions to keep interference from these communication nodes to a minimum. Unfortunately, this approach requires and consumes bandwidth that could otherwise be devoted to carrying data. Furthermore, this approach is not suitable for dynamic systems that often communicate at low elevation angles where multi-path interference causes rapid changes in signal intensity.
In a third approach, antennas are used which have large apertures. The larger aperture approach reduces the beam width of the communication node, which usually reduces interference to communication nodes that are not the intended targets of a transmission. However, this approach is not suitable for dynamic systems wherein communication nodes often move across the sky faster than a large antenna can steer. Furthermore, larger antennas cost more to purchase, install, and maintain, and are less suitable for use with a mobile node.
What is needed is a method that minimizes interference from a high-gain transmit antenna at one or more distant receiving nodes near the target node that is fast, non-expensive and which does not consume excessive bandwidth.